(1) Field of the Invention
This invention relates to a photocatalytic titanium dioxide powder, process for producing the same and applications thereof. More particularly, it relates to a photocatalytic powder comprising finely divided titanium dioxide particles having a coating of a substantially water-insoluble substance; a process for producing the photocatalytic powder; an organic polymer composition comprising the photocatalytic powder; a shaped article made of the polymer composition; and a structure having the photocatalytic powder on the surface thereof.
The photocatalytic titanium dioxide powder of the present invention is used as an environmental clarification material for removing malodor, decomposition-removing harmful substances or pollutants in air, treating drainage, purifying waste water, or performing sterilization or algicidal treatment of water. In particular, the photocatalytic titanium dioxide powder of the present invention is suitably used as an environmental clarification material by coating it on the surface of textile fiber, paper or plastic article, or incorporating it into textile fiber or plastic article at the step of producing the same, or used in the form of a coating material.
(2) Description of the Related Art
In recent years, photocatalysts using finely divided titanium dioxide particles are attracting attention as an environmental clarification material used for the purpose of antibacterial effect, deodorization, anti-staining or air or water clarification. The photocatalytic mechanism of the titanium dioxide is considered as follows. An electron and a hole generated inside the finely divided titanium dioxide particles convert water and oxygen present in the vicinity of the surface of the titanium dioxide particles into hydroxyl radical or hydrogen peroxide, and by virtue of the strong oxidation-reduction function of hydroxyl radical or hydrogen peroxide, harmful substances are converted into a harmless substance such as carbon dioxide gas, thereby attaining clarification. This photocatalytic action of finely divided titanium dioxide particles is said to permanently lasts as long as finely divided titanium dioxide particles, light, water and oxygen are present.
As applications of the titanium dioxide photocatalyst attempts are being made wherein the photocatalyst is incorporated in a medium having a shape suitable for handling such as fiber and plastic molded article, or a the surface of a substrate such as cloth and paper is coated with the photocatalyst. However, the strong photocatalytic action of titanium dioxide causes decomposition or degradation not only of harmful organic materials or environmental pollutants but also of the medium itself such as textile fiber, plastic and paper. This stands as an obstacle to the practical use of titanium dioxide photocatalyst. A coating material obtained by mixing finely divided titanium dioxide particles and a binder is drawing attention because of its good handling properties. However, an inexpensive binder exhibiting no adverse effect on the above-described medium has not yet been found out.
A process of allowing a photocatalytically inactive compound to be supported in the form of islands on the surface of titanium dioxide particles thereby suppressing the photocatalytic activity thereof so as to prevent or minimizing degradation of a plastic medium or a binder attributable to the activity of titanium dioxide particles is proposed in Japanese Unexamined Patent Application No. H9-225319 and H9-239277 (the term xe2x80x9cJapanese unexamined patent publicationxe2x80x9d is hereinafter abbreviated to xe2x80x9cJP-Axe2x80x9d). According to this process, the degradation of a plastic medium or a binder is reduced, but, the photocatalytically inactive compound directly adheres to the active site on the surface of titanium dioxide particles, therefore, it reduces the activity of the titanium dioxide particles as a photocatalyst, namely, it counteracts the photocatalytic activity thereof.
A photocatalyst comprising titanium dioxide particle, the surface of which is coated with porous calcium phosphate is proposed in JP-A H10-244166. This coated titanium dioxide particle has durability which is still poor under irradiation of a strong ultraviolet ray such as sunlight.
Further, in International Publication WO99/33566, there is disclosed a photocatalytic powder comprising finely divided titanium dioxide particles of which the surface is at least partially provided with a porous coating layer of calcium phosphate, with an anionic surfactant being present at the interface between the surface of titanium dioxide particle and the porous coating layer.
In view of the foregoing problems of the heretofore proposed techniques, an object of the present invention is to provide a photocatalytic titanium dioxide powder which can effectively and advantageously perform the environmental clarification, for example, which can remove malodor, decomposition-remove harmful substances or pollutants in air, treat drainage, purify waste water and impart bactericidal or antifungal properties, in particular, which deteriorates mediums such as textile fiber, paper or plastic shaped article only to a negligible extent and exhibits excellent durability for a long period of time when it is coated on textile fiber, paper or plastic shaped article, incorporated into fiber or plastic shaped article, or used in the form of a coating material.
Other objects of the present invention are to provide a process for producing the above-mentioned photocatalytic titanium dioxide powder, a polymer composition comprising an organic polymer and the photocatalytic titanium dioxide powder, a shaped article made of the polymer composition, and a structure having the photocatalytic powder on the surface thereof.
To sum up, the objects of the present invention are to provide a photocatalytic titanium dioxide powder capable of exhibiting durable photocatalytic activity in the environment irradiated with strong light such as sunlight, a polymer composition comprising the photocatalytic powder, a shaped article made of the polymer composition, and a structure having the photocatalytic powder on the surface thereof.
As a result of extensive researches, the present inventors have found that when a coating of a substantially water-insoluble organic substance is formed on the surface of finely divided titanium dioxide particle, the above-described objects can be achieved.
Thus, in one aspect of the present invention, there is provided a photocatalytic powder comprising finely divided titanium dioxide particles having a coating of a substantially water-insoluble organic substance formed on the surface of each titanium dioxide particle.
In another aspect of the present invention, there is provided a process for producing a photocatalytic powder, comprising the steps of (i) mixing a water-soluble organic substance and finely divided titanium dioxide particles in an aqueous medium to prepare a slurry; (ii) adding an insolubilizer such as, for example, a water-soluble calcium compound to the slurry to form a coating of an substantially water-insoluble organic substance on the surface of each titanium dioxide particle; and further, optionally, (iii) calcining the titanium dioxide particle having formed thereon the coating of an substantially water-insoluble organic substance at a temperature of about 100xc2x0 C. to about 800xc2x0 C.
In further aspects of the present invention, there are provided a polymer composition comprising an organic polymer and the above-mentioned photocatalytic powder comprising finely divided titanium dioxide particles having formed thereon a coating of an substantially water-insoluble organic substance; a shaped article made of the organic polymer composition; and a structure having the above-mentioned photocatalytic powder on the surface thereof.